CWQ Comments on Agency Analysis of Perchlorate Effects on People with Genetic Thyroid Disorders

An article published earlier this summer by researchers within the Agency for Toxic Substances and Disease Registry, a division of the Centers for Disease Control and Prevention, requires some clarifications in order to put the comments of the authors in context with the issue of determining safe levels of perchlorate exposure.

The article suggested it is plausible — but not confirmed — that ingestion of perchlorate could have health effects on people with genetic disorders of the thyroid. The article did not suggest what levels of perchlorate might be of concern.

In considering this analysis — which suggests only that future studies on perchlorate should consider the genetic makeup of the participant along with other variables — it is important to remember four key points:

  • Inasmuch as this agency analysis calls for more research, it is directly in line with the conclusions of a 2005 National Academy of Sciences (NAS) report, the “Health Implications of Perchlorate Ingestion.” (The NAS report can be viewed online at
  • While suggesting more research would be useful, the NAS report stated clearly that “the committee found that the data on perchlorate’s mechanism of action and effects in animals and humans are sufficient to derive a reference dose” that is protective of even the most vulnerable sensitive subpopulations (see page 122 of the NAS report).
  • NAS’ reference dose was set at a level which the panel concluded would not inhibit the thyroid’s ability to absorb iodide. The NAS report even goes as far as to say “However, a dose that does not inhibit thyroid iodide uptake will not affect thyroid function even in subjects with an abnormal thyroid gland or a very low iodide intake” (see p.44).
  • The NAS committee’s reference dose on perchlorate was based on a broad range of research, going back decades to perchlorate’s use as a medicine to treat thyroid disorders. The NAS committee also took testimony at a series of public hearings to ensure wide opportunity for input. The NAS panel stated and repeated frequently that it relied on many sources of information in reaching its conclusions. U.S. EPA then used the NAS conclusions to establish a Drinking Water Equivalent Level of 24.5 parts per billion for perchlorate.

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